It is generally accepted that the immune system and cellular immunity in particular are involved in the mechanisms affecting the outcome of gestation. In order to evaluate a putative role of lymphocytes in the immunological mechanisms of unexplained recurrent spontaneous abortions (URSA), we studied peripheral blood lymphocyte subpopulations in 244 women with URSA and 44 controls.Direct immunofluorescence in whole blood with the appropriate combinations of monoclonal antibodies and flow cytometry was used.The study showed: a) a statistically significant increase of the mean CD4/CD8 ratio (2.12+/-0.84 vs 1.85+/-0.63, P = 0,039); b) a statistically significant decrease of the mean value of the percentage of CD5+ CD19+ lymphocytes (0.4+/-0.6 vs 1.4+/-0.78, P or = 5%, where 5 equals the mean value + 2 standard deviations (SD) of the mean value of controls), whereas such a high percentage was not found in any control subject.It seems that women who experienced URSA comprise a heterogeneous population, as far as immunological parameters are concerned. At least in a subgroup of them, TCRgammadelta + T cells could be considered to play a role in the immune pathogenesis of fetal loss.